muskeltonus

Muskeltonus, or muscle tone, refers to the continuous and passive state of tension in skeletal muscles. It results from a combination of neural drive, reflex activity, and the viscoelastic properties of muscle and connective tissue. At rest, tone provides postural stability and readiness for movement and is regulated by spinal reflex circuits, especially the stretch reflex, and by supraspinal input from the brain.

Normal tone varies with age, activity, and emotional state. Hypotonia denotes abnormally low resistance to passive movement and can occur in certain congenital, neuromuscular, or central nervous system disorders. Hypertonia denotes increased resistance and can be velocity-dependent (spasticity) or non-velocity-dependent (rigidity). Other hypertonic conditions include dystonia, with sustained or intermittent abnormal postures, and paratonia, a passive resistance to movement.

Physiologically, muscle tone is shaped by the gamma motor system and muscle spindle sensitivity, modulated by motor cortex, basal ganglia, and cerebellar circuits. Damage to upper motor pathways, such as the corticospinal tract, often releases spinal reflexes and leads to spasticity, whereas other lesions can alter rigidity or dystonia.

Assessment relies on clinical examination of resistance to passive movement and movement quality, sometimes using scales such as the Modified Ashworth Scale or Tardieu scale. Electrophysiological measures and imaging may complement assessment. The presence and pattern of abnormal tone help localize lesions and guide therapy.

Common conditions with altered Muskeltonus include cerebral palsy, stroke, multiple sclerosis, spinal cord injury, and traumatic brain injury. Management aims to maintain range of motion and function through physical and occupational therapy, stretching, and positioning. Pharmacologic options include baclofen, tizanidine, diazepam, and dantrolene; botulinum toxin injections for focal spasticity; intrathecal baclofen for severe cases. Surgical approaches such as selective dorsal rhizotomy may be considered in select patients.